Eighteen inmates were injured Tuesday when fighting broke out among dozens of armed inmates at a maximum-security prison in Central California, corrections officials said.

One correctional officer hurt his back as he helped to break up the fight at Salinas Valley State Prison in Soledad, but he was not assaulted by inmates, said Terry Thornton, a spokeswoman for the California Department of Corrections and Rehabilitation. The prison is located about 130 miles southeast of San Francisco and holds nearly 3,600 inmates.

The guard was taken to an outside hospital, as were 11 of the injured inmates, she said. One of the injured inmates was airlifted to a hospital by helicopter.

Seven more inmates were treated at the prison.

The 18 inmates had "a variety of slash wounds and stab wounds and some head trauma," Thornton said. The inmate who was airlifted was stabbed in the head, she said.

She did not know the condition of the wounded inmates.

Of the 200 inmates in the exercise yard shortly before noon, 159 participated in the fighting, she said. Numerous inmate-made weapons were found later by guards who quelled the disturbance with pepper spray, tear gas and rubber bullets.

Most inmates were locked in their cells after the fight.

Thornton could not say what sparked the fighting or whether it was gang related. The cause was being investigated.